Capturing CO2 and flue gas carbon by Methanosarcina mazei Go1 and Methanothermobacter thermautotrophicus ΔH

Methane production from CO₂ and flue gas by Methanosarcina mazei Gö1 and Methanothermobacter thermautotrophicus ∆H was evaluated under various environmental and nutritional conditions to optimize methane production. M. thermautotrophicus exhibited optimal methane production at 60 °C, yielding 18.64 ± 0.75 μmol L⁻¹, whereas M. mazei demonstrated peak activity at 35 °C with CO₂ and 40 °C with flue gas, albeit with lower yields under thermophilic conditions. The optimal pH for M. thermautotrophicus was 5, producing 18.48 ± 0.75 μmol L⁻¹ of methane with CO₂, while M. mazei preferred a neutral pH for maximal methane production. Methane production in M. thermautotrophicus was significantly increased at 200 kPa, resulting in a methane content of 13.84 ± 0.55 μmol L⁻¹ with flue gas. Organic nitrogen sources significantly improved methane yields; peptone and soybean meal enhanced methane production to 18.64 ± 0.75 μmol L⁻¹ and 13.84 ± 0.55 μmol L⁻¹, respectively, in M. thermautotrophicus. Inorganic nitrogen sources, particularly NaNO₂, also supported higher methane production, achieving 11.70 ± 0.47 μmol L⁻¹ with flue gas. Phosphate and sulfate supplementation were critical; M. thermautotrophicus exhibited maximum activity with Na₂HPO₄ (3.35 ± 0.13 μmol L⁻¹) and FeSO₄ (7.98 ± 0.32 μmol L⁻¹) under CO₂ conditions. The optimal inoculum densities were determined to be 5–10 % for M. thermautotrophicus and 15 % for M. mazei. Therefore, the integration of these methanogens into biogas systems offers a promising approach for efficient CO₂ and flue gas conversion, indicating their potential for sustainable bioenergy production and greenhouse gas mitigation.